1. Field of the Invention
The present invention relates to an optical fiber and, more particularly, to a ferrule device for sealing a connector or other items fitted into the terminal end of the optical-fiber cable in order to hermetically package the optical fibers.
2. Description of the Related Art
In general, an optical fiber serves as an optical-signal-transmission medium used in an optical-communication system. By incorporating a wavelength-division-multiplexing technique in the optical-communication system, the optical system enables superhighway, high-capacity information to be transferred in long-distance communication, thus accelerating the flow of information in the optical-communication system.
A plurality of optical-fiber strands are bundled into a line of cables and used to establish a long-distance communication network. Here, at least two optical-fiber cables are connected to each other to provide the optical communication line. During operation, the optical line is subject to various environments, such as a hot-wet environment, an underwater environment, a toxic environment, or the like, which may have an adverse effect on the optical communication, in particular on a long-distance communication network. It is easy for the optical-fiber cables to be damaged through a tensile force or an external environment after the installation. As such, an inter-connector, such as a hermetic package or the like, between the optical-fiber cables is utilized to protect the fibers.
FIG. 1 shows a perspective view of a conventional hermetic packaging 100 used to couple optical fibers, and FIG. 2 depicts a sectional view of the hermetic packaging 100 shown in FIG. 1. As shown in FIGS. 1 and 2, the conventional hermetic packaging 100 for optical fibers comprises an optical-fiber block 110 serving as the terminal end of an optical-fiber cable, a case 120, and a ferrule 130 for the hermetic packaging.
The optical-fiber cable is shown as a ribbon-type optical-fiber cable 141 in which a plurality of optical-fiber strands are bundled to form a ribbon or band. In this ribbon-type optical-fiber cable 141, each of the optical-fiber strands is separated and aligned on the optical-fiber block 110 to be connected to the optical-fiber cable or another optical device at the other end.
The optical-fiber block 110 includes a lower block 113 provided with at least one V-shaped groove 115 for aligning each of the optical-fiber strands 142, and an upper-glass element 111 which is bonded on the lower block 113 by an adhesive, such as an epoxy or the like, together with the aligned optical-fiber strands 142 to protect the optical-fiber strands 142. This type of an optical-fiber block 110 is disclosed in detail in U.S. Pat. No. 6,118,917, filed on Sep. 12, 2000 and granted to the applicant, in which the optical-fiber block is manufactured by aligning each of the optical-fiber strands in the corresponding V-shaped grooves spaced apart in the same distance on a lower block, bonding an upper-glass element firmly and polishing the end surfaces of the optical-fiber strands to minimize a transfer loss.
The case 120 serves to prevent any foreign materials from penetrating the interior of the ribbon-type optical-fiber cable 141 when the outer sheath of the terminal end of the ribbon-type optical-fiber cable is removed to expose each of its strands 142. The case 120 also acts to protect the optical-fiber block 110 at the same time. Due to handling problems, the optical-fiber cable 141 is preferably connected with the optical-fiber block 110 first and then bonded with the case 120. Thus, the bonded portion of the case 120 must be provided with a passageway of sufficient size that the optical-fiber block 110 can pass through it.
If the passageway of the case 120 is too large, the 120 is not only unsuitable to bond directly with the ribbon-type optical-fiber cable 141 and is also prone to damage the optical-fiber cable in the portion to be bonded. For this reason, a ferrule 130 for the hermetic packaging comes to use, as explained with reference to FIGS. 3a to 5b. 
FIG. 3a is a perspective view of a ferrule 30 for hermetically packaging optical fibers according to one conventional embodiment. FIG. 3b is a sectional view of the ferrule 30 shown in FIG. 3a. As shown in FIGS. 3a and 3b, the ferrule 30 is provided with a hole 31, which extends in a longitudinal direction and through which a ribbon-type optical-fiber cable passes, and a soldering hole 31, which extends from the outer peripheral surface of the ferrule to the through hole 31. With the ferrule 30, the optical-fiber cable passes through the through hole 31, then the soldering hole 33 is injected with molten solder. Thereafter, the optical-fiber block is connected to the end of the optical-fiber cable and then the case is bonded with the ferrule 30, thereby completing the hermetic-packaging process.
However, the conventional ferrule has a drawback in that while the solder material is injected into the soldering hole, some foreign materials or gases are not perfectly removed from the hole so that air bubbles remain in the hole after the soldering process which leads to an incomplete seal.
FIG. 4 is a perspective view of a ferrule 40 for hermetically packaging optical fibers according to another conventional embodiment. As shown in FIG. 4, this ferrule 40 includes an upper body 43 and a lower body 41. First, a ribbon-type optical-fiber cable is arranged in a recess 45 of the lower body 41 and an adhesive is applied, then finally the upper body 43 is mated with the lower body 41. With this ferrule 40, there is an advantage in that it is easy to manufacture. However, there are disadvantages in that air bubbles still remain after the mating between the two bodies as it is impossible to achieve precise mating through the mating process between the upper body 43 and the lower body 41 due to a machining allowance of the components.
FIG. 5a is a perspective view of a ferrule 50 for hermetically packaging optical fibers according to yet another conventional embodiment, and FIG. 5b is a sectional view of the ferrule 50 shown in FIG. 5a. As shown in FIGS. 5a and 5b, the ferrule 50 is provided with a hole 51, which extends in a longitudinal direction and through which a ribbon-type optical-fiber cable passes, and two soldering holes 53 and 55 each extending from the outer peripheral surface of the ferrule to the hole 51. In this ferrule 50, the ribbon-type optical-fiber cable passes through the through hole 31 and then the soldering hole 33 is injected with molten solder. The optical-fiber block is connected to the end of the optical-fiber cable, then the case is bonded with the ferrule 50, thus completing the hermetic-packaging process. Here, any one of the soldering holes 53 and 55 is filled with molten solder, and the other acts to expel foreign materials or gases from the through hole. Therefore, this embodiment can attain a seal better than the prior embodiments. However, this ferrule 50 still has a drawback in that while the solder is injected into the soldering hole, foreign materials and gases are not completely removed from the through hole, so that the resulting hermetic packaging cannot satisfy the desired sealing quality.